Piston pump



FIG. 1 is a front perspective view of a piston pump showing my new design;

FIG. 2 is a top plan view thereof, the bottom being a mirror image of the top shown;

FIG. 3 is a rear elevational view thereof;

FIG. 4 is a front elevational view thereof; and

FIG. 5 is an elevational view taken from one side thereof, the opposite side being a mirror image of the side shown. 

The ornamental design for a piston pump, substantially as shown and described. 